The present invention generally relates to a method and apparatus for aligning an extraction electrode to an arc chamber of an ion implantation apparatus and more particularly, relates to a method and apparatus for aligning an extraction electrode to an arc chamber of an ion implantation machine by utilizing a simple calibration tool for aligning the slit openings of the electrode to the chamber.
Semiconductor fabrication processes often use a high current ion implantation machine to implant impurity ions into semiconductor substrates in order to form doped regions, such as sources and drains. The ion implanter delivers a beam of ions of a particular type and energy to the surface of a silicon substrate. Such machines typically include an ion source supply, normally a gas source, and an ion source power supply which is connected to an ion source head. A small quantity of the gas is passed through a vaporizer oven and then into an arc chamber which includes a heated filament, and an anti-cathode. The filament is directly heated by passing electric current through it, derived from the power supply. This heating causes thermionic emission of electrons from the surface of the filament.
An electric field, typically 30 to 150 volts is applied between the filament and the arc chamber walls using the power supply. The field accelerates the electrons in the filament area to the arc chamber walls. A magnetic field is then introduced perpendicular to the electric field to cause the electrons to spiral outward, increasing the path length and chances for collisions with the gas molecules. The collisions break apart many of the molecules and ionize the resultant atoms and molecules by knocking outer shell electrons out of place. As charged particles, these atomic or molecular ions can now be controlled by magnetic and/or electric fields.
Source magnets are employed to change the ion path from a straight path to a helicoid path. With one or more electrons missing, the particles carry a net positive charge. An extraction electrode (anti-cathode) placed in proximity to a slit and held at a negative potential attracts and accelerates the charged particles out of the chamber through the slit opening in the top of the chamber. Ions exiting the chamber are passed through an acceleration tube where they are accelerated to the implantation energy as they move from high voltage to ground. The accelerated ions form a beam well collimated by a set of apertures. The ion beam is then scattered over the surface of a wafer using electrostatic deflection plates.
After operation over a period of time, the processing of gasses in the arc chamber results in the accumulation of materials deposited from the gas, causing the formation of a conductive coating on the filament, chamber walls and anti-cathode. This coating eventually flakes, causing the filament to short out such that it can no longer produce electrons and the implantation machine becomes inoperable. This shorting phenomena is a result of arc-outs and typically occurs during boron implanting. When the arc chamber shorts out, it is necessary to clean the chamber, the anti-cathode and filament, which is a time consuming procedure since the machine is operated at a high vacuum pressure. This procedure is not only time consuming and costly, but the machine down time reduces throughput.
After the chamber and the chamber components such as the extraction electrode are cleaned, the components are put back into the chamber and an alignment process must be performed before the implanter can be put back into operation. Conventionally, the alignment process cannot be carried out under off-line conditions. It is difficult to control the tilt/align action of an extraction electrode by controlling the tilt/align motor controls located on a source control panel of the equipment. The calibration operation requires two technicians with one operating the control switches on the panel and the other observing the reaction of the electrode. Furthermore, the relative position of the slit opening in the extraction electrode and the slit opening in the arc chamber can only be observed by human eyes. It is difficult to identify whether the ion beam is aligned, thus causing a variety of mis-alignment problems. For instance, the same beam current may be generated by relatively higher arc current, rather than by the calibrated current. This leads to a shorter lifetime of the source head and also mis-alignment. Another problems caused is the high extraction current incurred and that the source chamber can be heavily coated with contaminants which reduces the cycle time for preventive maintenance as well as the available machine up-time. Other problems caused are the low quality beam current, out-of-specification monitoring and possibly extraction arcing.
A typical hot cathode penning discharge ion source 10 is shown in FIG. 1. The ion source 10 is constructed by an arc chamber 12, an extraction electrode 14 for the extraction of an ion beam 16, an ion source magnet power supply 18, deceleration power supply 20, extraction power supply 22, filament power supply 24, arc power supply 26 and vaporizer 28.
It is therefore an object of the present invention to provide a method for aligning an extraction electrode to an arc chamber of an ion implantation apparatus that does not have the drawbacks or the shortcomings of the conventional methods.
It is another object of the present invention to provide a method for aligning an extraction electrode to an arc chamber of an ion implantation apparatus by utilizing a simple mechanical calibration tool.
It is a further object of the present invention to provide a method for aligning an extraction electrode to an arc chamber of an ion implantation apparatus which can be carried out by a single technician.
It is another further object of the present invention to provide a method for aligning an extraction electrode to an arc chamber of an ion implantation apparatus by utilizing a calibration tool and a tilt/align controller.
It is still another object of the present invention to provide a method for aligning an extraction electrode to an arc chamber of an ion implantation apparatus by inserting a calibration tool into the slit openings in the extraction electrode and in the arc chamber.
It is yet another object of the present invention to provide a calibration tool for aligning an extraction electrode to an arc chamber of an ion implantation apparatus that is a simple mechanical tool in the shape of a flat key.
It is still another further object of the present invention to provide a calibration tool for aligning an extraction electrode to an arc chamber of an ion implantation apparatus which has the shape of a flat key with a base portion of a larger width and a tip portion of a smaller width.
In accordance with the present invention, a method and an apparatus for aligning an extraction electrode to an arc chamber of an ion implantation apparatus are provided.
In a preferred embodiment, a method for aligning an extraction electrode to an arc chamber of an ion implantation apparatus can be carried out by the operating steps of providing a calibration tool in the shape of a flat key having at least two reducing, stepped width from a base portion toward a tip portion of the key, the tip portion has a smaller width adapted for intimately engaging a slit opening in the arc chamber, while the base portion has a larger width adapted for intimately engaging a slit opening in the extraction electrode; tilting the extraction electrode and moving the extraction electrode horizontally by a tilt motor and an alignment motor, respectively; the tilt motor and alignment motor are controlled by a tilt/align controller; and inserting the calibration tool into the slit opening of the arc chamber through the slit opening of the extraction electrode, or repeating the steps until the insertion can be made.
The method for aligning an extraction electrode to an arc chamber of an ion implantation apparatus may further include the step of inserting the calibration tool through at least two slit openings in the extraction electrode, or the step of inserting the calibration tool through three slit openings in the extraction electrode. The method may further include the step of fabricating the calibration tool of a rigid plastic or metal, or fabricating the calibration tool of aluminum. The method may further include the step of fabricating the calibration tool in such a dimension that a width of a portion of the key is at least 0.3 mm smaller than a width of a corresponding slit opening that the portion of key is to be inserted, or the step of fabricating the calibration tool in such a dimension that a width of a portion of the key is about 0.5 mm smaller than a width of a corresponding slit opening that the portion of the key is to be inserted.
The present invention is further directed to a calibration tool for aligning an extraction electrode to an arc chamber of an ion implantation apparatus which includes a body in the shape of a flat key that has at least two reducing, stepped widths toward a tip portion of the key, the body further includes a base portion that has a larger width adapted for intimately engaging a slit opening in the extraction electrode; and a tip portion that has a smaller width adapted for intimately engaging a slit opening in the arc chamber.
In the calibration tool for aligning an extraction electrode to an arc chamber of an ion implantation apparatus, a width of the base portion is at least 0.3 mm smaller than a width of a corresponding slit opening in the extraction electrode. A width of the base portion may be about 0.5 mm smaller than a width of a corresponding slit opening in the extraction electrode. A width of the tip portion may be at least 0.3 mm smaller, and preferably about 0.5 mm smaller than a width of a corresponding slit opening in the arc chamber. The calibration tool may be fabricated of a rigid plastic or metal, or may be fabricated of aluminum.